Stress relieving through-silicon vias

ABSTRACT

Methods and systems for stress relieving through-silicon vias are disclosed and may include forming a semiconductor device comprising a stress relieving stepped through-silicon-via (TSV), said stress relieving stepped TSV being formed by: forming first mask layers on a top surface and a bottom surface of a silicon layer, forming a via hole through the silicon layer at exposed regions defined by the first mask layers, and removing the first mask layers. The formed via hole may be filled with metal, second mask layers may be formed covering top and bottom surfaces of the silicon layer and a portion of top and bottom surfaces of the metal filling the formed via hole, and metal may be removed from the top and bottom surfaces of the metal exposed by the second mask layers to a depth of less than half a thickness of the silicon layer.

FIELD

Certain embodiments of the disclosure relate to semiconductor chippackaging. More specifically, certain embodiments of the disclosurerelate to a method and system for stress relieving through-silicon vias.

BACKGROUND

Semiconductor packaging protects integrated circuits, or chips, fromphysical damage and external stresses. In addition, it can provide athermal conductance path to efficiently remove heat generated in a chip,and also provide electrical connections to other components such asprinted circuit boards, for example. Materials used for semiconductorpackaging typically comprises ceramic or plastic, and form-factors haveprogressed from ceramic flat packs and dual in-line packages to pin gridarrays and leadless chip carrier packages, among others.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present disclosure as set forth inthe remainder of the present application with reference to the drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic illustrating a semiconductor package utilizingstress-relieving through-silicon vias, in accordance with an exampleembodiment of the disclosure.

FIGS. 2A and 2B illustrate the effects of thermal mismatch in asemiconductor package, in accordance with an example embodiment of thedisclosure.

FIG. 3 illustrates a conventional through-silicon via and a stressrelieving through-silicon via, in accordance with an example embodimentof the disclosure.

FIGS. 4A-4F illustrate a process of forming a stress relievingthrough-silicon via, in accordance with an example embodiment of thedisclosure.

FIG. 5 illustrates example steps in fabricating a stress-relievingthrough-silicon via, in accordance with an example embodiment of thedisclosure.

DETAILED DESCRIPTION

Certain aspects of the disclosure may be found in stress relievingthrough-silicon vias. Example aspects of the disclosure may compriseforming a semiconductor device comprising a stress relieving steppedthrough-silicon-via (TSV), said stress relieving stepped TSV beingformed by: forming first mask layers on a top surface and a bottomsurface of a silicon layer, forming a via hole through the silicon layerat exposed regions defined by the first mask layers, and removing thefirst mask layers. The formed via hole may be filled with metal, secondmask layers may be formed covering top and bottom surfaces of thesilicon layer and a portion of top and bottom surfaces of the metalfilling the formed via hole, and metal may be removed from the top andbottom surfaces of the metal exposed by the second mask layers to adepth of less than half a thickness of the silicon layer. The secondmask layers may be removed and regions formed by the metal removing maybe filled with a conductive material, which may comprise polysilicon andthe metal may comprise copper. The stress relieving stepped TSV may beformed in an interposer and/or an integrated circuit die. The metal maybe removed utilizing an etching process or a laser ablating process. Adielectric layer may be formed on sidewalls of the formed via holebefore filling with metal. Half of the metal filling the vias may beexposed by the second mask layers.

FIG. 1 is a schematic illustrating a semiconductor package utilizingstress-relieving through-silicon vias, in accordance with an exampleembodiment of the disclosure. Referring to FIG. 1, there is shown apackage 100 comprising die 101, a packaging substrate 103, passivedevices 105, an interposer 107, solder balls 111, a lid 113, moldcompound 121, and thermal interface material 123.

The die 101 may comprise integrated circuit die that have been separatedfrom one or more semiconductor wafers. The die 101 may compriseelectrical circuitry such as digital signal processors (DSPs), networkprocessors, power management units, audio processors, RF circuitry,wireless baseband system-on-chip (SoC) processors, sensors, memory, andapplication specific integrated circuits, for example. In addition, thedie 101 may comprise micro-bumps 109 for providing electrical contactbetween the circuitry in the die 101 and contact pads on the surface ofthe interposer 107.

The interposer 107 may comprise a semiconductor substrate separated froma wafer, such as a silicon wafer, with through-silicon-vias (TSVs) 115that provide electrically conductive paths from one surface of theinterposer 107 to the opposite surface. TSVs may typically becylindrical in shape and made from copper, or similar metal, that has adifferent coefficient of thermal expansion (CTE) than the surroundingsilicon. This difference in CTE may result in stress in the silicon,which may affect the performance of nearby devices, such as when theTSVs are in a semiconductor die, or the electrical continuity ofinterconnects, such as when the TSVs are near redistribution layers inan interposer, for example, as illustrated in FIGS. 2A and 2B.

In an example scenario, the TSVs 115 may comprise stress-relievingfeatures that may comprise portions removed in both the top and bottomhalves of the TSV and backfilled with a material, such as polysilicon,for example. In this manner, displacement caused by different materialCTEs may be absorbed by the features in the TSVs 115.

The interposer 107 may also comprise backside bumps 117 for makingelectrical and mechanical contact to the packaging substrate 103. Inanother example scenario, the interposer 107 may comprise glass or anorganic laminate material, either of which may be capable of large panelformats on the order of 500×500 mm, for example.

The packaging substrate 103 may comprise a mechanical support structurefor the interposer 107, the die 101, the passive devices 105, and thelid 113. The packaging substrate 103 may comprise solder balls 111 onthe bottom surface for providing electrical contact to external devicesand circuits, for example. The packaging substrate 103 may also compriseconductive traces in a non-conductive material for providing conductivepaths from the solder balls to the die 101 via pads that are configuredto receive the backside bumps 117 on the interposer 107. Additionally,the packaging substrate 103 may comprise pads 119 for receiving thesolder balls 111. The pads 119 may comprise one or more under-bumpmetals, for example, for providing a proper electrical and mechanicalcontact between the packaging substrate 103 and the solder balls 111.

The passive devices 105 may comprise electrical devices such asresistors, capacitors, and inductors, for example, which may providefunctionality to devices and circuits in the die 101. The passivedevices 105 may comprise devices that may be difficult to integrate inthe integrated circuits in the die 101, such as high value capacitors orinductors. In another example scenario, the passive devices 105 maycomprise one or more crystal oscillators for providing one or more clocksignals to the die 101.

The lid 113 may provide a hermetic seal for the devices within thecavity defined by the lid 110 and the packaging substrate 103. A thermalinterface may be created for heat transfer out of the die 101 to the lid113 via the thermal interface material 123, which may also act as anadhesive.

FIGS. 2A and 2B illustrate the effects of thermal mismatch in asemiconductor package, in accordance with an example embodiment of thedisclosure. Referring to FIG. 2A, there is shown a semiconductor package200 comprising semiconductor die 201A and 201B, back end of line (BEOL)211A and 211B, and a bonding layer 219. The die 201A may comprise anintegrated circuit die with electronic devices, such as the CMOStransistor 203A, and the die 201B may comprise a CMOS device 203B. Onlyone device is shown for thermal strain illustrative purposes, as the die201A and 201B may comprise electrical circuitry such as digital signalprocessors (DSPs), network processors, power management units, audioprocessors, RF circuitry, wireless baseband system-on-chip (SoC)processors, sensors, memory, and application specific integratedcircuits, for example.

The BEOL 211A and 211B may comprise interconnect layers, such asredistribution layers 207A-207C, buried vias 205A-205C, and blind vias215. The redistribution layers 207A and 207B, buried vias 205A-205C, andblind vias 215 may provide electrical connectivity between devices inthe semiconductor die 201A and devices in other structures, such as thedie 201B, or external to the semiconductor package 200 for example.

The bonding layer 219 may comprise an adhesive layer that bonds the die201A/BEOL 211A to the die 201B/BEOL 211B, and may comprise conductivepillars 209 to provide electrical connection between the die/BEOLstructures. The conductive bumps 217 may comprise metal bumps or solderballs, for example, for bonding the semiconductor package 200 to anotherstructure such as a substrate or circuit board.

The die 201B may comprise TSVs 213 for providing an electricalinterconnect through the die 201B from the conductive pillars 209 to theredistribution layers 207C in the BEOL 211B. In an example scenario, thesilicon in the die 201B has a different CTE than the copper in the TSVs213, such that when the die 201B heats up in operation or due to theenvironment, thermal stresses in the lateral direction, as illustratedby the wide arrows extending from the TSVs 213, may affect performanceof nearby devices. For example, the CMOS device 203B may becompressively strained due to the laterally expanding TSVs 213, as shownby the reduced width of the CMOS device 203B, exaggerated forillustrative purposes, compared to the unstrained CMOS device 203A.

This strain from different CTEs may result in carrier mobilityvariations, which may be different for p- and n-type material and indifferent directions from the TSVs, and threshold voltage variations innearby semiconductor devices. Thus, even if the CMOS devices 203A and203B were nominally identical in design and manufacturing, the CMOSdevice 203B may have different performance when thermal shifts causestrain from the TSVs 213.

FIG. 2B illustrates the semiconductor package 200, with thesemiconductor die 201A and 201B, BEOL 211A and 211B, and bonding layer219, but demonstrates strain in the vertical direction. For example, theelectrical interconnections provided by the buried vias 205A and 205Band the redistribution layers 207A and 207B may be physically impairedby the strain due to thermal expansion. In an example scenario, theexpansion of the TSVs with temperature, as illustrated by the whitedownward-pointing arrow, may push on the conductive pillar 209, theredistribution layer 207B, the blind via 205B, and the redistributionlayer 207A, causing an open circuit at the intersection with the blindvia 205A.

In an example scenario, stress-relieving TSVs may be utilized to absorbthe mechanical strain cause by different CTEs of the semiconductor andmetal layers in the semiconductor package 200. For example, in formingthe TSVs 213, metal may be partially removed from the top and bottom andbackfilled with another material, resulting in a structure that iscapable of absorbing mechanical strain, reducing or eliminating strainon nearby electronic devices and/or electrical interconnects.

FIG. 3 illustrates a conventional through-silicon via and a stressrelieving through-silicon via, in accordance with an example embodimentof the disclosure. Referring to FIG. 3, there is shown a conventionalTSV 303 formed in the silicon layer 301 and a stress-relieving TSV 307formed in a silicon layer 305.

The conventional TSV 303 comprises a copper layer in a silicon layer301, which may comprise a silicon substrate. The different CTEs ofsilicon and copper may cause physical strain in the vicinity of the TSV303 due to thermal expansion or contraction. Expansion of theconventional TSV 303 may result in lateral strain in the silicon layer301 and vertical strain into structures coupled to the TSV 303.

The stress relieving TSV 303 may comprise a stepped structure, withmaterial partially removed from the top and bottom of the TSV 303. Thestepped structure may be operable to absorb physical strain from thermalexpansion since the remaining metal portion may move within the spacecreated by the removed metal, as illustrated by the arrows in the lowerright figure. In an example scenario, In addition, a different materialmay be backfilled in the removed portion, as illustrated in FIGS. 4A-4F.

FIGS. 4A-4F illustrate a process of forming a stress relievingthrough-silicon via, in accordance with an example embodiment of thedisclosure. The large arrows indicate the process flow from FIG. 4A to4D. Referring to FIG. 4A, there is shown a silicon layer 401 and masklayers 403A and 403B. The silicon layer 401 may comprise an integratedcircuit die or an interposer, for example. The mask layers 403A and 403Bmay comprise a patterned photoresist layer, or other suitable maskmaterial for the desired etching process, formed by photolithographytechniques, for example.

The silicon layer 401 may then be etched all the way through forming avia hole using an etching or ablating process, for example. The dashedlines in FIG. 4B illustrate that while the etching or ablating processextends all the way through the silicon layer 401, it is only in regionswhere TSVs are to be formed, i.e., the silicon layer 401 is notseparated into two wholly separate parts.

The mask layers 403A and 403B may be removed and the removed portion ofthe silicon layer 401 may then be filled with metal, such as with copperlayer 405, in a plating or deposition process, for example, asillustrated in FIG. 4C. In another example scenario, a thin dielectriclayer may be formed on the etched sidewalls prior to filling with metal.Second mask layers 403C and 403D may then be formed on the top andbottom surfaces of the silicon layer 401 to cover a portion of thecopper layer 405, as shown in FIG. 4D. While a copper layer is shown inFIGS. 4C-4F, other metals suitable for TSVs may be utilized.

The exposed portions of the copper layer 405 may be removed less than orequal to half the depth of the silicon layer from the top and bottomsurfaces, resulting in the stepped structure with the top portion 411,middle portion 413, and bottom portion 415 illustrated in FIG. 4E. Thecopper may be removed by an etching or laser ablating process, forexample. Finally, the removed portion of the copper layer 405 may thenbe backfilled with a filler material 407, which may comprisepolysilicon, for example. The filler material 407 may comprise aconductive material to ensure a low resistivity despite the reducedcopper thickness. In addition, the filler material 407 may be selectedto absorb any expansion of the remaining copper layer 405 or to providea different CTE material in the TSV. In an alternative scenario, thefiller material 407 may comprise a non-conductive material selected forits strain-absorbing properties.

The right view in FIG. 4F is a top view of the remaining copper layer405 and the filler material 407, both within the silicon layer 401. Inthis example, a cylindrical structure is shown, although other shapesmay be utilized. Note that a single step is shown and discussed forillustrative clarity, but a multi-step TSV structure may also be formed,for example using additional etching and/or filling steps.

FIG. 5 illustrates example steps in fabricating a stress-relievingthrough-silicon via, in accordance with an example embodiment of thedisclosure. In the first step 501, a mask layer may be formed on top andbottom surfaces of the silicon layer, followed by step 503, where theexposed regions of the silicon layer may be etched through forming a viahole.

In step 505, the mask layers may be stripped, followed by step 507 wherethe removed regions may be filled with metal, or alternatively firstcovered with a thin dielectric layer followed by filling with metal.

In step 509, the silicon layer and filled vias may be masked on top andbottom surfaces, exposing a portion of the metal. In step 511, the metalmay be removed in the exposed regions to a depth less than half of thesilicon layer, leaving a stepped via structure, followed by step 513where the etched vias may be filled with a polysilicon material, forexample.

In an embodiment of the disclosure, a method is disclosed for stressrelieving through-silicon vias. In this regard, aspects of thedisclosure may comprise forming a semiconductor device comprising astress relieving stepped through-silicon-via (TSV), said stressrelieving stepped TSV being formed by: forming first mask layers on atop surface and a bottom surface of a silicon layer, forming a viathrough the silicon layer at exposed regions defined by the first masklayers, and removing the first mask layers.

The formed via hole may be filled with metal, second mask layers may beformed covering top and bottom surfaces of the silicon layer and aportion of top and bottom surfaces of the metal filling the formed viahole, and metal may be removed from the top and bottom surfaces of themetal exposed by the second mask layers to a depth of less than half athickness of the silicon layer. The second mask layers may be removedand regions formed by the metal removing may be filled with a conductivematerial, which may comprise polysilicon and the metal may comprisecopper.

The stress relieving stepped TSV may be formed in an interposer and/oran integrated circuit die. The metal may be removed utilizing an etchingprocess or a laser ablating process. A dielectric layer may be formed onsidewalls of the formed via before filling with metal. Half of the metalfilling the formed via hole may be exposed by the second mask layers.

In an embodiment of the disclosure, a device is disclosed for stressrelieving through-silicon vias. In this regard, aspects of thedisclosure may comprise a stress relieving stepped through-silicon-via(TSV) in a silicon layer, the stress relieving stepped TSV comprising: avia hole formed through the silicon layer, metal partially filling afirst region of the formed via hole to a depth that is less than halfthe thickness of the silicon layer from a top surface of the siliconlayer, and metal partially filling a second region of the formed viahole to a depth that is less than half the thickness of the siliconlayer from a bottom surface of the silicon layer.

A cross-section of the first region of the formed via hole partiallyfilled from the top surface of the silicon layer is within half of across-sectional area of the stress relieving stepped TSV while across-section of the second region of the formed via hole filled fromthe bottom surface of the silicon layer is within an opposite half ofthe cross-sectional area of the stress relieving stepped TSV. Regions ofthe formed via hole not filled by metal may be filled with a secondconductive material.

The second conductive material may comprise polysilicon and the metalmay comprise copper. The stress relieving stepped TSV may be formed inan interposer and/or an integrated circuit die. A dielectric layer maybe formed between the metal and sidewalls of the formed via hole. Across-section of the stress-relieving stepped TSV may be circular. Across-section of the first region of the formed via hole may comprise afirst half of the circular cross-section of the stress relieving steppedTSV and a cross-section of the second region of the formed via hole maycomprise a second half of the circular cross-section of the stressrelieving stepped TSV.

While the disclosure has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present disclosure. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present disclosure without departing from itsscope. Therefore, it is intended that the present disclosure not belimited to the particular embodiments disclosed, but that the presentdisclosure will include all embodiments falling within the scope of theappended claims.

What is claimed is:
 1. A method for semiconductor packaging, the method comprising: forming a semiconductor device comprising a stepped through-silicon-via (TSV), said stepped TSV being formed, at least in part, by: providing a via hole through a silicon layer; filling the via hole with metal; and removing, from within the via hole, a portion of the metal in the via hole from top and bottom surfaces of the metal to a depth of less than half a thickness of the silicon layer; wherein said removing comprises: removing the metal from the top surface in a first cross-sectional area of the via hole while retaining the metal from the top surface in a second cross-sectional area of the via hole opposite the first cross-sectional area; and removing the metal from the bottom surface in the second cross-sectional area of the via hole while retaining the metal from the bottom surface in the first cross-sectional area.
 2. The method according to claim 1, comprising filling regions formed by the metal removing with a conductive material.
 3. The method according to claim 2, wherein the conductive material comprises polysilicon.
 4. The method according to claim 1, wherein the metal comprises copper.
 5. The method according to claim 1, comprising forming the stepped TSV in an interposer.
 6. The method according to claim 1, comprising forming the stepped TSV in an integrated circuit die.
 7. The method according to claim 1, comprising removing the portion of the metal from within the via hole utilizing an etching process.
 8. The method according to claim 1, comprising removing the portion of the metal from within the via hole utilizing a laser ablating process.
 9. The method according to claim 1, comprising forming a dielectric layer on sidewalls of the via hole before filling with metal.
 10. The method according to claim 1, wherein the metal filling a middle portion of the via hole comprises a step structure.
 11. A semiconductor device comprising: a stepped through-silicon-via (TSV) in a silicon layer, the stepped TSV comprising: a via hole that extends through the silicon layer, where the via hole comprises a top portion, a middle portion and a bottom portion along the longitudinal axis of the via hole; and a metal that extends longitudinally through the via hole; wherein the metal partially fills the top and bottom portions of the via hole less than the metal fills the middle portion of the via hole; wherein the metal in the top portion is within a first half of a cross-sectional area of the via hole and not in an opposite second half of the cross-sectional area of the via hole; and wherein the metal in the bottom portion is within the opposite second half of the cross-section area of the via hole and not in the first half of the cross-sectional area of the via hole.
 12. The semiconductor device according to claim 11, wherein regions of the via hole not filled by metal are filled with a filler material.
 13. The semiconductor device according to claim 12, wherein the filler material comprises polysilicon.
 14. The semiconductor device according to claim 11, wherein the metal comprises a step structure in the middle portion of the via hole.
 15. The semiconductor device according to claim 11, wherein the stepped TSV is in an interposer.
 16. The semiconductor device according to claim 11, wherein the stepped TSV is in an integrated circuit die.
 17. The semiconductor device according to claim 11, wherein a dielectric layer is between the metal and sidewalls of the via hole.
 18. The semiconductor device according to claim 11, wherein a cross-section of the via hole is circular.
 19. The semiconductor device according to claim 11, wherein the top and bottom portions are generally the same size and larger in the longitudinal direction than the middle portion.
 20. A semiconductor device comprising: a circular cross-section stepped via in a layer, the stepped via comprising: a via hole that extends through the layer, where the via hole comprises a top cylindrical portion, a middle cylindrical portion and a bottom cylindrical portion along the longitudinal axis of the via hole; and a metal that extends longitudinally through the via hole; wherein the metal partially fills the top and bottom cylindrical portions of the via hole less than the metal fills the middle cylindrical portion of the via hole; wherein the metal in the top cylindrical portion is within a first half of a cross-sectional area of the via hole and not in an opposite second half of the cross-sectional area of the via hole; and wherein the metal in the bottom cylindrical portion is within the opposite second half of the cross-section area of the via hole and not in the first half of the cross-sectional area of the via hole. 